The present invention relates to an optical pickup device which is advantageous when employed in, for example, an optical disk apparatus, a magneto-optic disk apparatus or the like.
Generally, a memory storage apparatus such as the optical disk apparatus, the magneto-optic disk apparatus or the like (hereinafter referred to as an “optical disk apparatus”) is provided with an optical pickup device for recording and/or reproducing data.
The optical pickup device is generally constructed by assembling optical components in a box. In order to incorporate this optical pickup device in a main body of the optical disk apparatus, it is necessary to make this box small-sized. For this reason, in a related optical pickup device, the optical components to be fixed in the box have been fixed only by adhesives or only with pressure by biasing members such as springs, without employing tight fixation members such as screws, nuts, small screws, etc.
Therefore, there has been such an anxiety that when the optical components, especially, a deflecting mirror or a deflecting prism are attached to the support box by the adhesives, they tend to be displaced from positions to be fixed to the box by shrinkage or expansion of the adhesives, resulting in deterioration in their accuracy, though the optical components have excellent accuracy by themselves. In the optical pickup device employing the optical components which have thus deteriorated in accuracy, there may happen, in some cases, such an inconvenience that a spot diameter of a beam or a direction of an optical axis cannot be always constant.
In order to solve such a problem, various methods have been proposed as methods for fixing the optical components. FIGS. 12 and 13 show one example of such methods.
FIG. 12 is a perspective view of a half mirror as a polarizing member in a state fixed to support frames of the optical pickup device, and FIG. 13 is a front view of the half mirror of FIG. 12.
The half mirror 100 is one of the components constituting the optical pickup device, and fixed to a pair of mounting frames 101, 102 by adhesives 103.
The half mirror 100 is formed in a shape of a rectangular parallelepiped thin plate having an incidence face 100A, an emitting face 100B, and four side faces 100C intersecting these faces.
The adhesives 103 are applied to one of the mounting frames 101 at two contact points, and to the other mounting frame 102 at two contact points, four contact points in total, and positioned near four apexes of the emitting face 100B, on the side faces 100C which are opposed with respect to the emitting face 100B. With this arrangement, an influence on the half mirror 100 by shrinkage or expansion of the adhesives 103 is intended to be decreased.
By the way, the half mirror 100 and the mounting frames 101, 102 have different thermal expansion coefficients because they are formed of different materials. For this reason, when heat is added to these members, there will occur expansions different in both the members. In particular, since the mounting frames 101, 102 are formed by die casting, the shrinkage and expansion of the mounting frames 101, 102 by thermal expansion are not constant because of materials, and they are sometimes displaced in a back and forth direction in FIG. 12. On such occasions, the emitting face 100B will be twisted and the adhesive 103 at one contact point among the adhesives 103 of the four contact points for fixing the half mirror 100 to the mounting frames 101, 102 is likely to be flaked off. It is concerned that an optical axis of the optical pickup device may be misaligned, in case where the adhesive has been flaked off.